1. Field of the Invention
The present invention relates to a lens barrel and an image pickup apparatus including a clutch mechanism that absorbs an impact from an outside of the lens barrel or the image pickup apparatus.
2. Description of the Related Art
Conventionally, a lens barrel and an image pickup apparatus capable of changing a focal length of an image pickup lens by extending each lens unit that constitute the image pickup lens toward an object side have been known. For example, when an external impact is applied to the lens barrel in an extended state of the image pickup lens, an excess load is applied to a gear that constitutes a transmission mechanism of a drive force. In this time, cogs of the gear may be chipped off and thus a stable operation of the lens barrel may be difficult.
Accordingly, a lens barrel which mounts a mechanism (an impact absorption mechanism) to prevent damages of the gear has been known. Commonly, the transmission mechanism of the drive force is configured to couple a motor with a barrel unit via a two-stage gear, and thus the drive force of the motor is transmitted to the barrel unit while the two-stage gear reduces the speed of the drive force.
Japanese Patent Laid-open No. 2002-195313 discloses an overload clutch device using a coil spring as an impact absorption mechanism. Specifically, the coil spring is disposed in a space provided inside one gear of two gears that constitute a two-stage gear. In this configuration, when a great force is applied to the gear, the gear spins out and thus the damages of the gear can be prevented. On the other hand, Japanese Patent Laid-open Nos. 2002-276693 and 2003-315655 disclose configurations of using a plate spring and a C-shaped spring instead of the coil spring.
However, in the configuration disclosed in Japanese Patent Laid-open No. 2002-195313, it is necessary to dispose the coil spring inside the gear, and thus the size of a clutch mechanism is enlarged. In addition, it is necessary to provide a member to prevent the coil spring from being released from the gear. In the configurations disclosed in Japanese Patent Laid-open Nos. 2002-276693 and 2003-315655, the plate spring and the C-shaped spring are disposed inside the gear, and thus the degree of freedom of designing the spring is small and it is difficult to achieve a stable clutch operation.